The conversion of carbon monoxide with steam into carbon dioxide and hydrogen, known as the water-gas shift process, is extensively utilized in chemical and petrochemical industries, such as in the production of hydrogen, carbonyl compound and ammonia. This process is usually carried out in the presence of a catalyst to improve its efficiency. Among the known catalysts, the Fe--Cr system catalysts and Cu--Zn system catalysts are not competent due to their sensitiveness to sulfides and susceptibility to high-level sulfides and hence the quick reduction in shift activity in such a case, especially for carbon monoxide feed gases made from heavy oil, coal and residual oil, which usually contain various levels of sulfides. As an approach to overcome such problems, the Co--Mo system catalysts have been proposed, of which the active components are the oxides or sulfides of cobalt or nickel and molybdenum or tungsten, and the active components are usually supported over a carrier such as alumina or zirconia. These catalysts achieve good activity for the conversion of carbon monoxide feed gas containing higher level of sulfides.
However, the Co--Mo system catalysts have their maximum conversion activity in the sulphidized condition, so these catalysts require certain level of sulfides contained in the feed gas to keep them in a sulphidized state, and can not tolerate a feed gas of low level of sulfides. In fact, the concentration of sulfides in the gases to be converted does not affect the reaction and there is practically no upper limit to this concentration. Moreover, these catalysts display low activity at a lower reaction temperature (see U.S. Pat. No. 3,529,935). Addition of alkali metal can improve the low-temperature activity (see E.P. Application 062,912), though when the alkali metal-containing catalysts are used under low sulfide level, high steam partial pressure and high temperature condition, the phases of the active components and the carrier degrade, giving rise to the collapse of the structure and the inactivation of the catalyst. Further, during the conversion process, the alkali metal promoter migrates and leaves from the catalysts, deposits on the surface of the pipes and the equipment, and leads to the accumulation of chloride on such surfaces and eventually to equipment failure.
Obviously, there still exists a need for a catalyst for the conversion of carbon monoxide, which is free of alkali metal, active at a relatively low reaction temperature and can keep active and stable under low sulfide level, high steam partial pressure and high temperature condition, thus providing a conversion process with high performance.